A process of the type mentioned in the foregoing can be derived from EP-A-0062685. The conventional process is a path-duplicating (playback) method, according to which, in at least one, usually several, master spinning process or processes executed by an expert in the spinning art, coordinate data characteristic for the thus-traversed positions of the spinning roller determined with the aid of position pickups are stored in an electronic NC or CNC control unit and processed by the latter to output data; by serial call-up of these data, X- and Y-coordinate drive units of the spinning machine can be actuated along the lines of tracing the route of the spinning roller determined in the master spinning process. First of all, the contour of the spinning chuck is scanned and a set of coordinate data characteristic for its contour is fed into the NC or CNC control unit; from these data, a safety curve is determined, for example by interpolation, marking the limit of closest-possible approach of the spinning roller toward the spinning chuck. In the conventional process, the contour of the spinning roller proper is utilized as the safety curve.
In accordance with the conventional process of EP-A-0062685, the stored data include, in addition to the coordinate data, also data characteristic for the operating pressures linked to the respective coordinates; these latter data are utilized in the spinning processes subsequently repeated with great frequency for feeding corresponding pressures into the coordinate drive units--hydraulic cylinders. This is done to avoid drawbacks inherent in known path repetition processes used merely with storage of the path coordinates with exploitation of the latter as the desired data for the path motion control of the spinning roller; such drawbacks are seen in that even minor deviations of the shape of the round blank to be subjected to the spinning machining step from a reference shape can lead to the result that an exact tracing of the stored revolution routes is impossible and thereby spun parts of a very differing quality can be produced. Accordingly, the conventional process operates with a three-dimensional set of route tracing data which itself is accompanied by considerable technical expenditure and--on account of the processing time required--causes additional time requirement for the spinning procedure.
The conventional process furthermore has the disadvantage that considerable errors can occur in the detection of the operating pressures of the coordinate drive cylinders during the master spinning process, as well as in their introduction into the control during the spinning processes performed for manufacturing a relatively large series of maximally identical spun parts; this can manifest itself in clearly recognizable quality differences in the surface characteristic of the thus-produced spun parts. It is true that "scattering" of the quality of the manufactured spun parts due to inaccuracies in pressure detection and metered application during the "learning" of the routes as well as during their control can be kept to a moderately low level by taking care when performing the master spinning process that the operating pressures in total are maintained at a constant value along the lines that the forces acting on the sheet-metal workpiece are kept extensively constant over the various revolutions; however, this poses considerable demands for the spinning expert entrusted with performing the master spinning process since this person, while steering the master spinning process "by hand", must not only monitor the workpiece and the spinning roller but also the pressure indications for the coordinate drive cylinders, which is difficult and taxing and normally requires that a master spinning process must be repeatedly performed until finally an optimum set of coordinate and pressure data has been determined. A master spinning process making it possible to use the conventional process with the result of a properly uniform quality of the spun parts thus is very time-consuming and can be conducted at all only by using a highly qualified and very experienced spinning expert.
Additional programming and control expenditure also arises when operating according to the conventional process when using a customary scanning head for scanning the outer contour of the spinning chuck as the safety curve, this scanning head comprising a scanning ball of a small diameter that can be deflected into two mutually perpendicular directions; this scanning ball--after defined deflection strokes--opens alternatively respectively one of two switches whereby the attainment of a certain position is being announced. In this case, especially with small thicknesses of the material of the finished spun part, even very minor inaccuracies in the path control of the spinning roller, the radius of curvature of which in the rolling generating point can be markedly different from the radius of curvature of the scanning ball, will be enough for causing undesirably high relative deviations from the desired thickness of the spun part.
Therefore, it is an object of the invention to improve a process of the type discussed hereinabove so that performance of the master spinning process is simplified and also conductance of the spinning steps required for manufacturing spun parts can be controlled with simpler technical means.
This object has been attained with regard to the process of the invention by the features described and claimed herein as well as by the features of the spinning lathe of the invention which is suitable for performing the process.
A path control of the spinning roller in this process and spinning lathe of the invention is obtained in a simple way by the accordingly provided type of operating control of the coordinate drive units in accordance with a follow-up control process working with electrically controlled reference position value presetting and mechanical actual position value acknowledgment. This control process permits monitoring of the follow-up route--the so-called lag error--of the coordinate drive units and monitoring of the follow-up route. The increase of this follow-up route past a threshold value .DELTA.S.sub.max is an indication of the fact that the forces necessary for forming the workpiece material are growing larger than beneficial for a "smooth" shaping of the material. Also providing advantageous path control are the measures, triggered when this threshold value of this follow-up route has been exceeded, of lowering the path-tracing speed of the spinning roller and/or the transition to a routing curve of the spinning roller corresponding to an enlargement of the distance of the spinning roller rolling-off point, measured normally to the outer contour of the spinning chuck, with respect to its previously governing desired value curve, until once more a value for the follow-up path has been reached which is compatible with a good quality of the spun part to be produced. This path control, even if in the master spinning process only an approximately optimum route has been determined, leads to a gentle machining of the workpiece and therefore in the final result also to a good quality of its surface characteristic which can be attained with good reproducibility. The "learning procedure" can thus be executed with a substantially lower time consumption.
By utilizing the spinning roller as a "scanning head", it is ensured in a simple way that, with utilization of the positional coordinates, linked to its contact with the scanning supporting points, as the "safety curve", any possibly flawed conversion calculations are avoided, i.e. the danger is reliably excluded that, with very thin thicknesses of the material of a spun part to be produced, the safety curve could be "exceeded" with the consequence of damage to the spinning chuck.
In combination therewith, it is also possible, thanks to the type of operating control of the coordinate drive units provided--in accordance with this invention--to utilize the drive cylinders of these units also for scanning the outer contour of the spinning chuck, as specified in greater detail below.
A procedure of the invention utilizes the path routing coordinates of one revolution of the spinning roller as the reference path coordinates for a subsequent spinning process as set forth herein. This procedure permits an optimum route of the path of motion of the spinning roller in a few steps of path correction. In combination with an automatic control of this version of the process, a "self-programming" of the electronic control unit is readily possible, leading to an optimum track for the spinning roller in preliminary spinning steps as well as in a final spinning procedure.
It is then also possible, as provided in more detail hereinafter, to determine the desired course of a contour of the spun part along which the spinning roller moves solely by its numerical presetting.
A safety measure which ensures optimum protection of the spinning chuck is also provided according to the invention by adding coordinate increments to the scanning coordinate data to produce a set of coordinate data corresponding to a safety contour in a manner described more fully herein.
Additional features of the invention described hereinafter indicate a kind of scanning of the outer contour of the spinning chuck by means of the coordinate drive unit which also yields data on the evolution of the follow-up path along the route-tracing curves; these data can be evaluated in a simple way so that it is possible to maintain, during the spinning process, a constant or almost constant amount of the follow-up path which, in turn, provides the possibility in a simple way of controlling the motion control of the spinning roller in dependence on essentially one value of a maximum follow-up path .DELTA.S.sub.max.
Corresponding remarks apply analogously to a further procedure of the invention which is provided as an alternative to the aforementioned steps, namely to detect the follow-up path and to evaluate same with a view toward controlling the route with a substantially constant follow-up path.
In the embodiment of a spinning lathe provided according to the invention as set forth herein, the spinning lathe is suitable for performing the process of this invention and, monitoring of limit values of the follow-up path can take place in a simple way, for example with the aid of limit switches responding starting with a minimum deflection .epsilon. of the valve-operating members of the follow-up control valves pertaining to the coordinate drive units.
In the embodiment of such a spinning lathe, it is possible to effect a continuous detection of the follow-up path so that, for various phases of the spinning process, it is possible also to choose different limit values of the follow-up path, and when such values are exceeded, changes can be triggered in the route-tracing speed and/or changes in the route geometry.
In case several spinning rollers with a differing geometry of their rolling shoulders are provided for producing a spun part, it is advantageous to scan the spinning chuck with each one of these different spinning rollers, thus accordingly determining so to speak a separate safety curve for each of these spinning rollers.
Additional details and features of the process of this invention and of a spinning machine suitable for its performance can be seen from the following description of a specific embodiment of such a spinning machine with reference to the drawings and the explanation of its function.